Magnetic torque devices



H. w. sAMo Oct. 21,1958.

MAGNETIC TORQUE DEVICES Filed Nov. 10,1955

. INVENTOR. j HARVEY w. sAMo BY &

ATTORNEY United States atent MAGNETTC TORQUE DEVICES Harvey W. Samo, Bayonne, N. J., assignor to Dial Prod- .lyicts Company, Bayonne, N. 1., a corporation of New ersey Application November 10, 1955, Serial No. 546,053

8 Claims. (Cl. 192-34 Ihe invention relates generally to magnetic torque devices such as brakes and clutches which include a pair of magnetic members arranged for attraction toward each other by magnetization of the magnetic members.

Frictional type magnetic brakes and clutches generally include a magnet body having a coil winding disposed therein and a rotatable magnetic pole piece or armature mounted for axial movement toward and away from the magnet body. The magnet body and armature may have their axially opposed surfaces or pole faces spaced from each other 'by an air-gap. Upon energization of the magnet body a magnetic flux circuit is created which causes the pole faces of the magnet members to directly engage each other. Devices of this type furnish substantial torque output for power input, and are best suited for on and ofi service. Although such devices may be variously constructed to allow for the dissipation of heat, they are not suitable where uniform and substantially constant slip torque is desired, as for example, for accurate tension control units. The relative movement between the frictionally engaged metallic pole faces is not sufiiciently uniform to provide reliable results, particularly fits insofar as obtaining accurately controlled values of slip torque.

A common magnetic slip torque device now in use operates upon the principle of impressing a magnetic flux across a fixed air-gap between axially fixed magnetic members; there is no frictional contact between the magnetic members. The relative position of the magnetic members is such that resistance against relative movement or slip is due to a hysteresis effect which is dependent upon the spacing between the members and the density of the magnetic flux. Such devices must be constructed with extreme precision and care, because the airgap spacing is very critical, and must be maintained to a very close tolerance. A small change in the air-gap spacing will cause a considerable change in the output torque. This requires accurate micrometer adjustments and precision bearings, which make the product quite expensive. Moreover, if the product is not ruggedly constructed it may be put out of adjustment.

A primary object of my invention is to provide a magnetic slip torque device, either a brake or clutch,'of simple and rugged construction, which is inexpensive to manufacture.

Another object of my invention is to provide a magnetic torque device constructed to furnish uniform and substantially constant slip which may be quickly, easily and accurately adjusted to desired values at either the point of use or the point of manufacture of the product. Accurate adjustment of the air-gap may be so simply accomplished that it can be properly done by personnel untrained in the art of brake and clutch manufacture.

Still another object of the invention is to provide means for converting a common or usual type of magnetic fricice tion clutch or brake to a slip clutch or brake, thereby eliminating the necessity for manufacturing-and stocking additional product types. This convertibility feature permits inventory to be kept to a minimum, and is, therefore,

' economically advantageous.

' accordance with my invention;

Fig. 2 is a plan view of the brake shown in Fig. 1, illustrating the means for adjusting and fixing the air-gap spacing between magnetic members;

Fig. 3 is an enlarged, vertical sectional view, showing the. relationship between the magnetic members when spaced from each other by the air-gap spacing means of modifi'cation wherein the armature is also provided with a ring of a non-magnetic material; and

Fig; 7 is a side elevational view, partly in section, showing the invention as applied to an electromagnetic clutch.

Generally, my invention involves mounting a ring A providing aworking face of non-magnetic, wear-resistant material upon the outer periphery of one of a pair of magnetic members B and C of a common or usual frictional magnetic brake or clutch. A portion of the ring extends beyond the axial surface or pole face of the magnetic member upon which it is mounted for engagement by the opposite magnetic member when a magnetic flux .is produced causing the magnetic members to be attracted toward each other. The distance the ring extends in an axial direction beyond its underlying pole face determines the air-gap spacing between the magnetic members. The

.ring is preferably mounted for controlled movement in an axial direction so that the air-gap spacing may be adjusted to the length desired. The ring is then secured in desired position.

The ring A, or its working face, is formed of a tough, hard, wear-resistant material, which preferably has a low coefficient of friction. Plastic materials such as a molded fluoroethylene polymer or a polyamide, examples of which are Teflon and nylon, respectively, manufactured by the du Pont Company, are particularly suitable. The ring may also comprise a section of metal tubingplated with chromium, a non-magnetic metal which is hard, wearresistant and characterized by a low coefiicient of friction.

In greater detail, and referring to Figs. 1 to 4 for one embodiment of a magnetic slip torque device of my invention, a brake is provided which comprises a magnet body B and an armature C. The magnet body includes an annular cup-shaped metal shell 10 of magnetic material secured to an inner shaft 12, extending centrally therethrough. The shell and shaft are connected to each other as by swaging the shaft to the shell at 14. A coil winding 16 is disposedwithin the shell and surrounding the shaft 12. The coil is secured in place by confining it between a shoulder 18 formed on the shaft and a snap ring 20 on the opposite side (Fig. 3). Leads 22, 22 are provided for connection to a source of current. The magnetic cup-like shell provides a substantially annular pole face 24.

The magnetic member C is the usual armature having the form of a circular disc and provides a pole face 26. The armature may be a single unitary piece, or may comprlse a plurality of segments which together provide the circular disc. The armature is provided with equidistantly spaced, headed pins 28 secured at their stem ends to the armature disc, the pins passing, with clearance, through apertures 30 in the flange portion of a hub 32. This arrangement allows the armature to slide in an axial direction toward and away from the magnet body B. The hub is provided with a tapped hole 34 to receive a set screw for securing a shaft (not shown) to the hub for rotation therewith and the armature.

The device thus far described is a magnetic friction brake of usual construction. The magnet body B may be bolted to a fixed flange 36 to maintain the magnet body in fixed position. Upon energization of the coil 16, a magnetic flux circuit is created across the air-gap, designated 38, between the magnetic members, to cause the pole faces 24 and 26 to engage each other. When a shaft having a pulley thereon is connected to the hub 32, and a rotational force or tension is applied which exceeds the force causing the attraction between the pole faces 24 and 26, the rotatable pole face 26 will slip with respect to the fixed pole face 24. i

In an ordinary magnetic friction brake, the armature C has an outside diameter equal to the outside diameter of the cup-shaped shell 10. In accordance with this embodiment of the invention, the armature is made with an increased diameter to compensate for the thickness of the working face 40 of the ring A, mounted on or encircling the shell 10. The armature thus has an outer diameter substantially equal to the outer diameter of the ring. The ring A has its forward portion 42 extending in an axial direction beyond the pole face 24 by a desired amount which fixes the length of the air-gap 38. The ring A is secured to the shell by means of a set screw 44 passing through an opening or slot 46 in the ring and into a tapped hole 48 extending at least partially into the shell'wall.

The ring A is preferably arranged for controlled movement in an axial direction so that the length of the airgap 38 may be closely and accurately adjusted, after which the ring is secured in desired adjusted position. For this purpose, a cam slot and pin arrangement is provided. The ring is formed with a camming slot 50 within which is received an upstanding pin 52 secured to the wall of the shell 10. The camming slot is formed to extend at a slight angle, designated a in Fig. 2, with respect'to the working face 40.

For many applications, the length of the air-gap is critical, and requires fine adjustment. An example of a suitable arrangement may include the slot 50 having a length of one inch at an angle a of one degree and twentysix minutes (1 26) with respect to a plane perpendicular to the circumference of the ring. Turning or rotating the ring about the magnet body, in the direction indicated by the arrows (Fig. 2), will cause the ring to move in an axial direction a total of 0.025 inch. For a given size of brake, this amount of air-gap spacing may be the maximum distance desired. For intermediate air-gap spacings, a scale 54 may be provided on the ring along the length of the slot for alignment of its lines with a point of reference provided by the pin. A datum line 56 may be cut in the top of the pin 52. For the example given, adjacent lines on the scale may represent axial movement of 0.0025 inch by subdividing the length of the one inch carnming slot in tenths of an inch. The slot 46 may be made at the same angle as the angle of the camming slot 50. The entire amount of axial movement of the ring, however, is generally so small that the slot 46 may be straight or coincident with the circumference of the ring, as shown, with a width suflicient to provide clearance from the set screw 44 to allow for total axial movement of the ring. It is only necessary that the head of the set screw be of sufficient size to bear against the material of the ring adjacent the slot in any position of the ring.

In the construction shown, the ring is provided with a second set of securing and camming slots 46' and 50' on its diametrically opposite side for cooperation with set screws 44 and 52, respectively. This duplication is unnecessary in a brake, but is highly desirable in a clutch, where the magnet body is rotatable, and uniform distribution of mass is important.

The length of the air-gap 38 may be easily adjusted to the desired amount by rotating the readily accessible ring A to desired position and securing or fastening the ring in place by means of the set screw 44. Upon energization of the coil winding 16, the pole face 26 of the armature C engages the working face 40 of the ring.

Fig. 5 shows a modified form of ring wherein the ring, designated A, comprises a tubular or ring holder portion 58, preferably of a non-magnetic metal such as brass or aluminum, formed at its forward edge with a slot 60 within which is received, by a press fit, the stud-like end 62 of a non-magnetic, wear-resistant plastic ring 64 having a low coefficient of friction, such as the aforementioned molded nylon or Teflon. The slight resiliency of the plastic material permits a secure force fit, although if desired, the metal may be swaged against the stud portion 62 for additional holding purposes.

Referring to Fig. 6, the armature C, instead of having an outer diameter equivalent to the diameter of the shell 10 plus the thickness of the ring A as shown in Figs. 1 to 4, may have a diameter the same as the diameter of the shell 10, as is common or usual in magnetic friction brakes. In this embodiment, a ring 66 of nonmagnetic, wear-resistant material having a low coefiicient of friction, such as nylon or Teflon, may be secured around the circumference of the armature C for engagement with the forward edge of the ring A. The ring 66 has a thickness substantially equal to the thickness of the ring A. This arrangement provides frictional contact between a pair of non-magnetic, non-metallic surfaces having excellent wearing qualities and low coefficients of friction, and is particularly suitable for fine and accurately controlled slip torque. In addition, only slight modification of standard parts by addition is necessary. The magnet body and armature are the same as for a usual brake of the metal to metal friction variety.

Fig. 7 illustrates the invention as applied to a clutch. The magnetic members A and B and their relationship to each are essentially the same as described in connection with the brake, except that the magnetic member B is provided with a longer and hollow shaft 68 to receive a slip ring assembly 70 fixedly secured to the shaft as by a snap ring 72, the other side bearing against the cup-like shell. Of course, the magnet body B instead of being fixedly mounted on a support will be mounted in axially fixed position for rotation so that when current is impressed on the coil through the medium of brushes (not shown) engaging the conductive portions of the slip ring assembly, the magnet body B, as well as the armature C, may rotate.

The clutch illustrated shows an air-gap spacing and armature engaging ring A, as illustrated in Figs. 1, 2, and 4. It will be obvious that a ring as shown in Fig. 5 may be used. An armature provided with a ring around its circumference, as shown in Fig. 6, is also contemplated.

While the forms of the invention illustrated show the air-gap spacing ring mounted upon the magnet body of a magnetic brake or clutch, it will be apparent that the ring may instead be mounted on the armature. In this form of the invention, the armature would be of a greater width than illustrated in order to allow space for the means for permitting controlled axial movement of the ring toward the pole face of the magnet body which it would engage.

It is also within the scope of the invention to use the various ring structures described in combination with magnetic members of the permanent magnet type. The closely controlled spacing function furnished by the described rings is useful for magnetic torque devices of this type.

The described air-gap spacing means is suitable for accurately controlling the length of air-gap, in magnetic torque devices operating upon the hysteresis efiect principle. Although the air-gap spacing rings are engaged by the opposite magnetic member, the effect of friction may be kept small. The ring material may possess a low coefl'icient of friction coupled with excellent wear-resistant properties permitting the area of engagement to be kept to a The small frictional effect may be compensated for by adjusting the length of air-gap and power input, and advantage taken of the simple and accurate spacing function supplied by the ring. The described ring and magnetic member relationship permits easily adjustable and accurate control of air-gap length between the magnetic members, because the air-gap spacing ring is movable as a complete unit which at all times provides a working surface which is parallel to the pole faces. As a result, the expensive precision alignment means normally required for magnetic torque devices of this type is obviated.

It will be apparent that the electromagnetic slip torque devices described, with the readily accessible ring means for accurately controlling the length of gap mechanically may furnish a substantial range of torque output. By adjusting the electrical power input, fine adjustment within the range may then be obtained. Thus, a multiplicity of my magnetic torque device may have their air-gaps set at a given length, and all the devices may be adjusted together by regulating the power input from a single control.

The accessibility of the described means for mechanically adjusting and fixing the length of air-gap permits simple and easy adjustment at all times. This allows adjustment of the air-gap length to be made after some degree of wear of the engaging surfaces has taken place.

It will be apparent that numerous modifications may be made to the specifically described and preferred forms of the invention illustrated. Various changes may be made 1n the structures disclosed without departing from the scope of the invention as sought to be defined in the following claims.

I claim:

1. A magnetic slip torque device comprising a pair of members of magnetic material providing opposed pole faces, means operable when activated to produce a magnetic flux through said magnetic members to cause them to be attracted toward each other, means for fixing the air-gap spacing between said members and for furnishing substantially uniform slip torque, said means comprising a ring of non-magnetic, wear-resistant material having a lower coeflicient of friction than said members of magnetic material mounted on the outer periphery of one of said magnetic members and having a portion thereof extending beyond the underlying pole face, the amount said ring extends beyond said pole face providing the desired air-gap spacing between the magnetic members, the opposite magnetic member providing a surface for slip engagement with said ring when a magnetic flux is produced, and means for securing said ring to the magnetic member upon which it is mounted.

2. A magnetic slip torque device comprising a pair of members of magnetic material providing opposed pole faces, means operable when activated to produce a magnetic flux through said magnetic members to cause them to be attracted toward each other, means for adjusting and fixing the air-gap spacing between said members and for furnishing substantially uniform slip torque, said means comprising a ring of non-magnetic, wear-resistant material having a lower coeflicient of friction than said members of magnetic material slideably mounted on the outer periphery of one of said magnetic members, cooperating means provided by the ring and the magnetic member upon which it is mounted, whereby relative rotational movement between the ring and magnetic member will cause the ring to move in an axial direction toward the opposite magnetic member, a portion of said ring being moveable to a position beyond the underlying pole face to provide the desired air-gap spacing between the magnetic members, said opposite magnetic member providing a surface for slip engagement with said ring when a magnetic flux is produced, and means for securing said ring in desired adjusted position.

3. A magnetic slip torque device comprising a magnet body and an armature providing axially opposed pole faces, means slideably supporting the armature for axial movement toward and away from the magnet body, means associated with the magnet body and operable when activated to produce a magnetic flux through the magnet body and armature to cause them to be attracted toward each other, means for adjusting and fixing the airgap spacing between the magnet body and armature and for furnishing substantially uniform slip torque, said means comprising a ring of non-magnetic, wear-resistant material having a lower coeflicient of friction than said members of magnetic material slideably mounted on the outer periphery of the magnet body, cooperating means provided by the ring and the magnet body, whereby relative rotational movement between the ring and magnet body will cause the ring to move in an axial direction toward and away from the armature, a portion of said ring being moveable to a position beyond the underlying pole face to provide the desired air-gap spacing between the magnet body and armature, the armature providing a surface for slip engagement with said ring when a magnetic flux is produced, and means for securing said ring in desired adjusted position.

4. A magnetic torque device as set forth in claim 1, wherein the ring is formed of a material selected from the group consisting of fluoroethylene polymers and polyamides.

5. A magnetic torque device as set forth in claim 2, wherein the ring is formed of a material selected from the group consisting of fluoroethylene polymers and polyamides.

6. A magnetic torque device as set forth in claim 3, wherein the ring is formed of a material selected from the group consisting of fluoroethylene polymers and polyamides.

7. A magnetic torque device as set forth in claim 3,

wherein the outer diameters of the magnet body and the armature are substantially equal, and the armature is provided with a second ring of non-magnetic, wear-resistant material having a lower coeflicient of friction than said members of magnetic material secured to its circumference for engagement with the ring onthe magnet body.

8. A magnetic torque device as set forth in' claim 3,

wherein the outer diameters of the magnet body and the armature are substantially equal, and the armature is provided with a second ring secured to its circumference for engagement with the ring on the magnetbody, said rings being formed of a material selected from the group consisting of fluoroethylene polymers and polyamides.

References Cited in the file of this patent UNITED STATES PATENTS Taggart June 21, 1955 

